The present invention relates to a method and device for controlling a plasma-jet spark plug that produces a plasma by a spark discharge to ignite an air-fuel mixture in an internal combustion engine.
A spark plug is widely used in an automotive internal combustion engine to ignite an air-fuel mixture by spark discharge. In response to the recent demand for high engine output and fuel efficiency, it is desired that the spark plug increase in ignitability to achieve quick combustion and proper lean mixture ignition.
Japanese Laid-Open Patent Publication No. 57-2470 discloses, as one example of high-ignitability spark plug, a plasma-jet spark plug that has an electrical insulator made of e.g. ceramic and a pair of center and ground electrodes defining therebetween a discharge gap surrounded with the electrical insulator to produce a plasma by a spark discharge in the discharge gap through the application of a high voltage between the center and ground electrodes. The plasma is ejected to an air-fuel mixture through an opening of the discharge gap so as to induce ignition of the air-fuel mixture at a distance away from the ground electrode. The plasma-jet spark plug is thus able to limit the quenching effect of the ground electrode for improvement in ignitability.